1. Field of the Invention
The present invention relates to a magnetic material that is employed as a high performance permanent magnet and a manufacturing method of the same, and a bonded magnet using the same.
2. Description of the Related Art
So far, as a kind of a high performance permanent magnet, a rare earth magnet such as a Smxe2x80x94Co system magnet, a Ndxe2x80x94Fexe2x80x94B system magnet or the like is known. In these magnets, a large amount of Fe and/or Co is included and contributes to an increase of saturation magnetization. In addition, rare earth elements such as Nd and Sm, due to the behavior of 4f electrons in a crystal field, renders a very large magnetocrystalline anisotropy. Thereby, an increase of coercive force is obtained.
Such a rare earth system high performance magnet is mainly used for electrical appliances such as a speaker, a motor, a measurement instrument or the like. Recently, demand for smaller size of various kinds of electrical appliances is high. Accordingly, a high performance permanent magnet is demanded to cope with this demand. For these demands, a Fexe2x80x94Rxe2x80x94N system magnet (R is one element selected from Y, Th and Lanthanoid elements)(cf. Japanese Patent Application KOKOKU Publication No. Hei 5-082041 and so on) is proposed. However, it does not necessarily have sufficient characteristics.
Further, Japanese Patent Application KOKAI Publication No. Hei 8-191006 discloses a Rxe2x80x94Zrxe2x80x94Fe (Co)xe2x80x94N system magnetic material (R: rare earth element) in which a phase having a Th2Ni17 crystal structure (hereinafter refers to as Th2Ni17 crystal phase) is a principal phase. The Th2Ni17 crystal phase, compared with a phase having a Th2Zn17 crystal structure (Th2Zn17 type crystal phase), can include a larger amount of Fe and/or Co. Accordingly, a magnetic material having the Th2Ni17 crystal phase as its principal phase is expected as a promising forming material of a permanent magnet in which the saturation magnetization or the like is further improved.
However, the magnetic material, of which principal phase is the Th2Ni17 crystal phase, obtained by the conventional manufacturing method has a disadvantage that its grain is relatively coarse. As a method for making fine grain, as disclosed in Japanese Patent Application KOKAI Publication No. Hei 8-191006, there are a rapid quenching method and a mechanical alloying method. However, these methods are disadvantageous from standpoints of improvement of manufacturing efficiency and reduction of manufacturing cost.
On the other hand, in the Rxe2x80x94Fexe2x80x94B system magnetic material, as a means for obtaining a fine grain, a HDDR (Hydrogenation-Disproportionation-Desorption-Recombination) method is known (cf. Japanese Patent Application KOKAI Publication No. Hei 1-132106). The HDDR method will be described in the following. In the case of the Rxe2x80x94Fexe2x80x94B system magnetic material, for instance, first, a Rxe2x80x94Fexe2x80x94B system mother alloy of which principal phase is R2Fe14B phase is heat treated in an atmosphere of hydrogen to transform into respective phases of RHX, Fe2B, and Fe. Then, in a dehydrogenation process, H2is removed from the material to form again the R2Fe14B phase. Thus obtained alloy has a recrystallization texture of which principal phase is a fine R2Fe14B phase of an average grain diameter of approximately 0.05 to 3 xcexcm. Thus, the HDDR method enables to obtain a fine texture only by an atmosphere treatment in an electric furnace, accordingly, from the standpoint of the manufacturing cost, is advantageous.
There are several reports in which the HDDR method is applied in magnetic material other than the Rxe2x80x94Fexe2x80x94B system. Mat.Chem.Phys.32, 280 to 285 (1992), for instance, discloses a Sm2Fe17NX system magnetic material of which principal phase is the Th2Zn17 crystal phase and which is prepared by use of the HDDR method.
Further, Japanese Patent Application KOKAI Publication No. Hei 8-037122 discloses a manufacturing method of a magnetic material where, a Rxe2x80x94Mxe2x80x94T system alloy (R: rare earth element, M: metallic element such as Al, Ti, V, Cr or the like, T: Fe, Fexe2x80x94Co) of which principal phase is the Th2Zn17 crystal phase is first HDDR treated, thereafter, nitrogenized to prepare a Rxe2x80x94Mxe2x80x94Txe2x80x94N system magnetic material of which principal phase is the Th2Zn17 crystal phase or a TbCu7 crystal phase. Further, in Japanese Patent Application KOKAI Publication No. Hei 4-260302, an alloy having a crystal structure of R2(T,M)17 system (R: rare earth element, T: Fe or Fexe2x80x94Co, M: metallic element such as Zr, Hf, Nb, Ta or the like) is exposed to the HDDR treatment.
All the HDDR treatments disclosed in these Patent Publications are given to the alloys of which principal phases are the Th2Zn17 crystal phase. Further, in Japanese Patent Application KOKAI Publication No. Hei 8-037122, an anisotropic magnetic material is obtained. Incidentally, in Japanese Patent Application KOKAI Publication No. Hei 4-260302, in order to invest an anisotropy to a magnetic material, the M element is added, and the crystal structure of the magnetic material is described as the R2(T,M)17 type. In the absence of the M, the crystal structure is the Th2Zn17 type, also in the presence of the M, similarly the crystal structure is considered to be the Th2Zn17 type.
Thus, though the HDDR method is known as a technique for making fine grain of the magnetic material, there is no disclosure in which the HDDR method is applied to the magnetic material that contains the Th2Ni17 type crystal phase as an indispensable component.
Therefore, an object of the present invention is to provide a magnetic material that is, by making fine grain of a magnetic material having the Th2Ni17 type crystal phase as an indispensable component, enhanced in magnetic characteristics, and a manufacturing method thereof. Further, another object is to provide a high performance bonded magnet that employs such a magnetic material.
The present inventors have eagerly studied to accomplish the aforementioned objects. As a result of this, the inventors found that even to a mother alloy having the Th2Ni17 type crystal phase (a phase having the Th2Ni17 type crystal structure) as a principal phase, the HDDR method is effective. By giving the HDDR treatment to a mother alloy having the Th2Ni17 type crystal phase as a principal phase, a magnetic material that includes the Th2Ni17 type crystal phase as an indispensable component and has a fine recrystallization texture can be obtained.
The present invention was accomplished based on this finding. A magnetic material of the present invention is characterized in that it has a composition expressed by the following general formula,
general formula:
{(R1XR21-X)YBZT1-Y-Z}1-QNQ 
(where, R1 is at least one kind of element selected from rare earth elements, R2 is at least one kind of element selected from Zr, Hf, Ti and Sc, T is at least one kind of element selected from Fe and Co, and X, Y, Z and Q denote numerical values satisfying 0.5xe2x89xa6X less than 1, 0.05xe2x89xa6Yxe2x89xa60.2, 0xe2x89xa6Zxe2x89xa60.1 and 0.1xe2x89xa6Qxe2x89xa60.2), and includes 5 volume % or more of the Th2Ni17 type crystal phase, and the average grain diameter of the magnetic material is in the range of from 0.02 to 50 xcexcm.
The magnetic material of the present invention has a recrystallization texture due to absorption and desorption of hydrogen. More specific, the magnetic material of the present invention has a recrystallization texture obtained through recrystallization due to the absorption and desorption of hydrogen by a mother alloy having the Th2Ni17 type crystal phase as a principal phase. The magnetic material of the present invention is particularly preferable to have the Th2Ni17 type crystal phase as a principal phase, however, depending on the manufacturing conditions, a magnetic material of which the principal phase is the Th2Zn17 type crystal phase or the TbCu7 type crystal phase can be obtained. The magnetic material of the present invention is preferable to further include a small quantity of boron. The content of boron is preferable to be in the range of 0 less than Zxe2x89xa60.1 as the value of Z.
A manufacturing method of a magnetic material of the present invention comprises steps of preparing a mother alloy having the Th2Ni17 type crystal phase as a principal phase, of recrystallizing, by letting the mother alloy absorb and desorb hydrogen, the mother alloy, and of preparing, by letting the recrystallized mother alloy absorb nitrogen, a magnetic material.
In the manufacturing method of the magnetic material of the present invention, a mother alloy is preferable to have a composition expressed by the following general formula,
general formula:
(R1XR21-X)YBZT1-Y-Z 
(where, R1 is at least one kind of element selected from rare earth elements, R2 is at least one kind of element selected from Zr, Hf and Sc, T is at least one kind of element selected from Fe and Co, and X, Y, and Z denote numerical values satisfying 0.5xe2x89xa6X less than 1, 0.05xe2x89xa6Yxe2x89xa60.2, and 0xe2x89xa6Zxe2x89xa60.1).
A bonded magnet of the present invention comprises a mixture of the aforementioned magnetic material of the present invention and a binder, and is characterized in that the mixture has a formed body of a magnet shape.
This invention is disclosed in Japanese Patent Application No. 10-081726 filed on March 27, 1998, and the entire disclosure thereof is incorporated herein by reference.
In the following, embodiments for carrying out the present invention will be described.
A magnetic material of the present invention has a composition expressed by the following general formula,
general formula:
{(R1XR21-X)YBZT1-Y-Z}1-QNQxe2x80x83xe2x80x83(1) 
(where, R1 is at least one kind of element selected from rare earth elements, R2 is at least one kind of element selected from Zr, Hf, Ti and Sc, T is at least one kind of element selected from Fe and Co, and X, Y, Z and Q denote numerical values satisfying 0.5xe2x89xa6X less than 1, 0.05xe2x89xa6Yxe2x89xa60.2, 0xe2x89xa6Zxe2x89xa60.1 and 0.1xe2x89xa6Qxe2x89xa60.2), and includes 5 volume % or more of a Th2Ni17 type crystal phase (a phase having the Th2Ni17 type crystal structure), and the average grain diameter of the magnetic material is in the range of from 0.02 to 50 xcexcm.
First, the reasons for compounding the respective components constituting the magnetic material of the present invention and for defining compounding amount will be described.
Rare earth elements as the R1 element are components that give a great magnetic anisotropy, accordingly a high coercive force, to a magnetic material. As such the R1 element, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, Y or the like can be cited. Among them, it is preferable in particular for Sm to be 50 atomic % or more of the R1 element. Thereby, the magnetic anisotropy of the principal phase is enhanced to increase the coercive force thereof.
The R2 element is at least one kind of element selected from Zr, Hf, Ti and Sc. Such the R2 element has advantages such as reducing an average atomic radius of the rare earth sites by occupying the rare earth sites of the principal phase. Thus, the R2 element plays an important role for obtaining the Th2Ni17 type crystal structure.
Ordinarily, it is known that in a binary alloy between Rxe2x80x94T (T is Fe or Co), in the case of employing Ce, Pr, Nd, Sm, and Gd as the R element, the Th2Zn17 type crystal phase is obtained, and in the case of employing Tb, Dy, Ho, Er, Eu, Tm, Yb, Lu, and Y as the R element, the Th2Ni17 type crystal phase is obtained. By compounding R2 element to such a system, even when Sm or Nd is employed as the R element (R1 element), the Th2Ni17 type crystal phase is obtained. Further, the R2 element suppresses precipitation of xcex1xe2x80x94Fe phase in the manufacturing process of the magnetic material to result in enhancement of the magnetic property.
In the aforementioned formula (1), the total amount of the R1 element and R2 element Y is designated in the range of 0.05xe2x89xa6Yxe2x89xa60.2. This is because by increasing the total amount Y of the R1 element and the R2 element, the large magnetic anisotropy is obtained to result in giving a high coercive force. However, when the R1 element and the R2 element are compounded too much, a magnetization is deteriorated. Therefore, the value of Y is preferable to be in the range of 0.09xe2x89xa6Yxe2x89xa60.15.
In addition, the increase of the ratio X of the R1 element to the total amount of the R1 element and the R2 element is advantageous for obtaining the high coercive force. Therefore, the value of X is designated in the range of 0.5xe2x89xa6X less than 1. However, when the ratio of the R1 element is too large, the Th2Ni17 type crystal phase is difficult to obtain. In the case of obtaining a magnetic material of which principal phase is the Th2Ni1, type crystal phase, the value of X is preferable to be in the range of 0.5xe2x89xa6Xxe2x89xa60.85. The value of X is more preferable to be in the range of 0.65xe2x89xa6Xxe2x89xa60.85.
The T element is at least one kind of element selected from Fe and Co, and plays a role of increasing a saturation magnetization of the magnetic material. The increase of the saturation magnetization leads to an increase of a residual magnetization, and accompanying it, the maximum magnetic energy product also increases. Such the T element is preferable to be included 70 atomic % or more in the magnetic material, thereby the saturation magnetization can be effectively increased. Further, in further increasing the saturation magnetization of the magnetic material, 50 atomic % or more of the T element is preferable to be Fe.
A part of the T element may be replaced by at least one kind of element (M element) selected from V, Cr, Mo, W, Mn, Ga, Al, Sn, Ta, Nb, Si and Ni. By replacing a part of the T element with the M element, the magnetic property can be improved, and together with this, various practically important characteristics such as corrosion resistance, heat resistance or the like can be improved. However, when too much of the T element is replaced by the M element, since the deterioration of the magnetic characteristics becomes remarkable on the contrary, the replacement amount of the T element by the M element is preferable to be designated 20 atomic % or less.
In the magnetic material of the present invention, B (boron) is not necessarily required to be compounded. However, by compounding B, the treatment condition when the HDDR treatment that will be described later is implemented can be made loose, and the alloy texture (recrystallization texture) can be made more homogeneous and fine. Further, B shows an effect of suppressing the precipitation of an xcex1xe2x80x94Fe phase or the like. Thereby, the residual magnetization and the maximum energy product of the magnetic material can be enhanced.
From the above description, the content of B is preferable to be in the range of 0 less than Zxe2x89xa60.1 as the value of Z in the formula (1). When the value of Z that denotes the content of B exceeds 0.1, in the heat treatment step, the amount of formation of R2Fe14B phase or the like increases to result in the deterioration of the magnetic property. The value of Z is more preferable to be 0.05 or less. Further, for the compounding of B to be more effective, the value of Z is further more preferable to be 0.005 or more.
N (nitrogen) mainly exists in the interstitial sites of the principal phase, and plays a role of, when compared with the absence of N, improving the Curie temperature and magnetocrystalline anisotropy of the principal phase. Among them, the improvement of the magnetocrystalline anisotropy is important in giving a large coercive force to the magnetic material. Though the N exhibits its effect with a small quantity, if too much of it is included, an amorphous phase or an xcex1xe2x80x94Fe phase tends to form, resulting in a deterioration of the magnetic characteristics of the magnetic material. Accordingly, the value of Q that shows the content of the N is designated in the range of 0.1xe2x89xa6Qxe2x89xa60.2. The value of Q is more preferable to be in the range of 0.14xe2x89xa6Qxe2x89xa60.18.
A part of the N may be replaced by hydrogen (H). In some cases, the H is introduced into the magnetic material by the heat treatment based on the HDDR method that will be described later, and exists mainly in interstitial sites of the principal phase similarly with the N. The H contributes in improving the magnetic property such as the coercive force or the like. However, since too much replacement of the H decreases the improvement effect of the Curie temperature or the magnetocrystalline anisotropy of the principal phase, the replacement amount of the N by the H is preferable to be 50 atomic % or less. Further, a part of the N may be replaced by C or P. The replacement amount in this case is designated 50 atomic % or less of the N including the replacement amount of the H. A part of the N (50 atomic % or less) may be replaced by at least one kind element (X element) selected from H, C and P.
Incidentally, the magnetic material expressed by the aforementioned formula (1) allows to contain an avoidable impurity such as an oxide or the like.
The magnetic material of the present invention having the aforementioned composition includes 5 volume % or more of the Th2Ni17 type crystal phase, and has a fine crystal texture of an average grain diameter of in the range of from 0.02 to 50 xcexcm. In particular, the magnetic material of the present invention is preferable to have the Th2Ni17 type crystal phase as the principal phase. Incidentally, the principal phase here indicates one that has the largest volume ratio among the constituent phases of the alloy. Such magnetic materials can be obtained, as will be described later, by implementing the HDDR treatment to the mother alloy of which principal phase is the Th2Ni17 type crystal phase.
The Th2Ni17 type crystal phase, compared with, for instance, the TbCu7 type crystal phase, has a high coercive force. Further, the Th2Ni17 type crystal phase can include much more Fe or Co (T element) than the Th2Zn17 type crystal phase. For instance, when Sm and Fe are used as the R1 and T elements, respectively, the Th2Zn17 type crystal phase has a small solid solution region. The Fe exceeding the stoichiometric ratio of 2:17 (Sm2Fe17 phase) precipitates as the xcex1xe2x80x94Fe phase or the like. This deteriorates the magnetic property. On the other hand, the Th2Ni17 type crystal phase extends its solid solution region into Fe rich side, accordingly, even if there is a little more Fe than the stoichiometric ratio of 2:17, the Th2Ni17 type crystal phase can be formed. In concrete, even if the composition ratio is approximately Sm2Fe17-19, the Th2Ni17 type crystal phase is formed. Thereby, in addition to an enhancement of the magnetic flux density, the crystal phase such as the xcex1xe2x80x94Fe phase or the like that deteriorates the magnetic characteristics can be suppressed from precipitating.
The Th2Ni17 type crystal phase contributes greatly in enhancing the high performance of the magnetic material. From these, the magnetic material of the present invention includes at least 5% or more by volume ratio of the Th2Ni17 type crystal phase. When the volume ratio of the Th2Ni17 type crystal phase is less than 5% among the constituent phases of the magnetic material, an excellent magnetic characteristic can not be obtained. Further, in order to utilize fully the property that the Th2Ni17 type crystal phase possesses and to enhance higher performance of the magnetic material, the magnetic material of the present invention has the Th2Ni17 type crystal phase as the principal phase. In more concrete, it is preferable to include 50% or more by volume ratio of the Th2Ni17 type crystal phase. The Th2Ni17 type crystal phase is more preferable to be included 80% or more by volume ratio. Incidentally, the constituent phases of the magnetic material can be checked by use of X-ray diffraction or the like.
The magnetic material of the present invention includes at least 5% or more by volume ratio of the Th2Ni17 type crystal phase, furthermore has a fine recrystallization texture based on the HDDR treatment, that is, the recrystallization texture due to absorption and desorption of hydrogen. The recrystallization texture due to the absorption and desorption of the hydrogen is fine and excellent in homogeneity, and can give an average grain diameter in the range of from 0.02 to 50 xcexcm. By reducing the average grain diameter of the magnetic material to 50 xcexcm or less, the coercive force and the residual magnetization can be enhanced. The average grain diameter of the magnetic material of the present invention is more preferable to be 10 xcexcm or less. However, when the average grain diameter is less than 0.02 xcexcm, there occurs a disadvantage such as a difficulty in investment of the magnetism. The average grain diameter of the recrystallization texture is particularly preferable to be in the range of from 0.02 to 1 xcexcm.
Measuring method of the average grain diameter of the principal phase of the present invention will be described below.
A transmission electron microphotograph of a metallic texture of a permanent magnet material is taken. When a cross section of a grain of TbCu7 phase observed on the microphotograph is designated as Sn (xcexcm3), the grain diameter rn (xcexcm) is defined by the following equation.
rn=2xc3x97({square root over ( )}Sn)/xcfx80
An average grain diameter t (xcexcm) is an averaged value of the respective grain diameters rn, that is, it is defined by the following equation.
t=(1/N)xc3x97xcexa3rn 
Here, N is a number of measurement of grain diameter. In the present invention, the number of measurement N is preferable to be 60 or more.
The magnetic material containing at least 5% or more by volume ratio of the Th2Ni17 type crystal phase, furthermore, the magnetic material of which principal phase is the Th2Ni17 type crystal phase, as described above, has an excellent magnetic characteristics such as the high saturation magnetic flux density or the like. In addition, by making a fine crystal texture (recrystallization texture) of the average grain diameter in the range of from 0.02 to 50 xcexcm, the coercive force, the residual magnetization or the like can be enhanced. Thus, the magnetic material of the present invention is to enhance furthermore the magnetic characteristics, therewith can cope with smaller size and higher performance of various kinds of electric component.
Now, the principal phase of the magnetic material of the present invention is not necessarily restricted to the Th2Ni17 type crystal phase. Depending on the compositions of the mother alloy thereon the HDDR treatment is carried out, the HDDR treatment condition, or the nitrogenization condition, the Th2Zn17, TbCu7, or ThMn12 type crystal phases can be the principal phase. Anyway, the Th2Ni17 type crystal phase is included at least 5% or more by volume ratio. When the amount of the R2 element in the mother alloy is made relatively scarce, the Th2Zn17 type crystal phase tends to appear. Further, in the case of Ti being much among the R2 elements or the M element that replaces a part of the T element being made much, the TbCu7 or ThMn12 type crystal phase tends to appear.
The principal phase of the magnetic material of the present invention can be selected according to usage. For instance, in the case of a high residual magnetization and maximum energy product being demanded, the Th2Ni17 type crystal phase is preferable to be the principal phase. For a magnetic material in which a high coercive force is asked for, the Th2Zn17 type crystal phase is preferable to be the principal phase. For a magnetic material in which a high thermal stability is asked for, the TbCu7 or ThMn12 type crystal phase can be made the principal phase. The principal phase here is one of the largest volume ratio among the constituent phases of the alloy, in concrete, is preferable to be 50% or more by volume ratio.
The volume occupancy of each phase existing in a magnetic material can be obtained from a transmission electron microphotograph of a cross section of the magnetic material by use of an areal analysis method.
With ratio of cross sections due to the areal analysis method, the volume occupancy can be expressed approximately. The volume occupancy of the present invention is an averaged values of 10 points.
The magnetic material of the present invention is manufactured, for instance, in the following manner.
First, an ingot including the prescribed amounts of the respective elements of R1, R2and T, further, as the need arises, B and M element, is prepared by an arc melting or a high-frequency melting. This mother alloy has the Th2Ni17 type crystal phase as a principal phase. To such an alloy ingot, as the need arises, in an inert gas atmosphere such as Ar, He or the like or in a vacuum, heat treatment is given under the conditions of the temperature in the range of approximately from 300 to 1200xc2x0 C. and the time period in the range of from 0.1 to 200 hours. By implementing such a heat treatment, a mother alloy with less precipitation of an xcex1xe2x80x94Fe phase is obtained.
The mother alloy that is used in preparation of the magnetic material of the present invention is preferable to have a composition expressed by the following general formula,
general formula:
(R1XR21-X)YBZT1-Y-Zxe2x80x83xe2x80x83(2) 
(where, R1 is at least one kind of element selected from the rare earth elements, R2 is at least one kind of element selected from Zr, Hf, Ti and Sc, T is at least one kind of element selected from Fe and Co, and X, Y, and Z designate numerical values satisfying 0.5xe2x89xa6X less than 1, 0.05xe2x89xa6Yxe2x89xa60.2, and 0xe2x89xa6Zxe2x89xa60.1).
By satisfying such an alloy composition, the principal phase of the mother alloy can be easily made the Th2Ni17 type crystal phase. However, notwithstanding the same alloy composition, depending on the preparation conditions, the crystal phase can be different. Accordingly, by controlling the condition of implementation of the heat treatment or the like after the mother alloy is melted and forged, the principal phase of the mother alloy is made the Th2Ni17 type crystal phase.
Thereafter, the obtained mother alloy is pulverized to be an average particle diameter of approximately several tens xcexcm to several hundreds xcexcm by use of a ball mill, a brown mill, a stamping mill or the like. To such the mother alloy powder, the step of recrystallization due to absorption and desorption of hydrogen is carried out. That is to say, a HDDR (Hydrogenation-Disproportionation-Desorption-Recombination) treatment is given. The Th2Ni17 type crystal phase, as mentioned above, extends its solid solution region in an Fe rich side. Thereby, the phase that deteriorates the magnetic characteristics such as an xcex1xe2x80x94Fe phase or the like can be suppressed from precipitating. As a result of this, after the HDDR treatment, the magnetic material that is scarce in the xcex1xe2x80x94Fe phase or the like and excellent in performance can be prepared with reproducibility.
In the HDDR treatment, first, the powder of the mother alloy is heat treated at the temperature in the range of approximately from 650 to 800xc2x0 C. in an atmosphere of a hydrogen gas for approximately from 30 min to 1 hour, to result in an absorption of hydrogen by the mother alloy. By this hydrogen absorption step, the Th2Ni17 type crystal phase decomposes into a RH phase, an xcex1xe2x80x94Fe phase or the like, and at the same time the crystal texture is made fine.
Next, while maintaining the same temperature, or while raising the temperature approximately from several tens to 100xc2x0 C., the evacuation is carried out to dehydrogenate. Thereafter, it is cooled to the room temperature. By this dehydrogenation, a crystal phase including at least 5% by volume ratio or more of the Th2Ni17 type crystal phase is recrystallized. The crystal phase due to this recrystallization texture maintains the fine texture due to the absorption of hydrogen. Therefore, the fine crystal texture (recrystallization texture) of the average grain diameter in the range of 0.02 to 50 xcexcm, further in the range of 0.02 to xcexcm can be obtained.
The constituent phases of the recrystallization texture are the Th2Ni17 type crystal phase, the Th2Zn17 type crystal phase, the TbCu, type crystal phase, the ThMn12 type crystal phase or the like. The Th2Ni17 type crystal phase is included at least 5% by volume ratio or more. Though the principal phase of the recrystallized phase can be one of the aforementioned four kinds of the crystal phases, as mentioned above, to obtain the magnetic material of high saturation magnetic flux density or high performance, the Th2Ni17 type crystal phase is preferable to be the principal phase.
Thereafter, the alloy powder undergone the recrystallization due to absorption and desorption of the hydrogen is heat treated in an atmosphere containing nitrogen (nitrogenation), thereby the aimed powder like magnetic material can be obtained. Thus obtained magnetic material is isotropic magnetic particles. The nitrogenation is preferable to be carried out under the temperature condition of 400 to 500xc2x0 C. in the atmosphere of nitrogen gas of the pressure of 0.01 to 10 atmosphere. The time period of the nitrogenation under these conditions is preferable to be 0.1 to 300 hours.
The atmosphere during the nitrogenation may be, in the place of the nitrogen gas, a nitrogen compound gas such as an ammonia gas or the like can be employed. When the ammonia gas is employed, the reaction rate of the nitrogenation can be enhanced. In this case, the simultaneous use of a gas such as hydrogen, nitrogen, Ar or the like can control the reaction rate of the nitrogenation.
In the aforementioned manufacturing method of the present invention, since the HDDR treatment is given to the mother alloy of which the principal phase is the Th2Ni17 type crystal phase, the magnetic material of high performance that has less xcex1xe2x80x94Fe phase and a fine recrystallization texture can be obtained. Though the fine texture can be obtained also by a rapid cooling method, by omitting the rapid cooling step, manufacturing efficiency of the magnetic material can be improved and the manufacturing cost can be reduced. There is also such an advantage that the recrystallization texture of fine and homogeneous texture can be easily obtained. Further, the magnetic material having the fine Th2Ni17 type crystal phase as the principal phase can be obtained with reproducibility.
The magnetic material of the present invention is suitable for a constituent material of, for instance, a bonded magnet. In the following, a manufacturing method of a bonded magnet from the magnetic material of the present invention will be described. Incidentally, when a bonded magnet is prepared, normally, a magnetic material is pulverized. However, when the magnetic material has been pulverized in the aforementioned preparation step, this step can be omitted.
(a). The powder of the magnetic material of the present invention is mixed with an organic binder. The obtained mixture is molded into a desired shape by compression molding or injection molding to obtain a bonded magnet. As the binder, for instance, an epoxy based, a nylon-based resin or the like can be used. When a thermosetting resin such as the epoxy based resin is used as the binder, after molding into the desired shape, it is preferable to cure at the temperature of from 100 to 200xc2x0 C. Incidentally, when a bonded magnet is prepared by the compression molding, by aligning crystal orientation under a magnetic field during pressurization, a permanent magnet of high magnetic flux density can be prepared.
(b). The powder of the magnetic material of the present invention, after being mixed with a low melt metal or a low melt alloy, is molded by the compression molding to prepare a metal bonded magnet. In this case, the low melt metal or the low melt alloy plays a role of the binder. As the low melt metal, for instance, Al, Pb, Sn, Zn, Cu, Mg or the like can be used, and as the low melt alloy, the alloys including the aforementioned low melt metals or the like can be used. In this case also, by aligning the crystal orientation under a magnetic field, a permanent magnet of high magnetic flux density can be prepared.
The specific embodiments of the present invention will be described below.
Embodiment 1 to 8
First, the respective raw materials of high purity are compounded with the prescribed ratio and melted by high frequency melting in an Ar atmosphere to prepare the mother alloy ingots, respectively. Next, the respective ingots of the mother alloys are heat treated in a vacuum under a condition of 1100xc2x0 C.xc3x9748 hours, and, thereafter, pulverized by a ball mill in the Ar atmosphere to be the average particle size of approximately 4 to 5 xcexcm. Upon carrying out the X-ray diffraction of the respective mother alloys, all are confirmed to have the Th2Ni17 type crystal phase as the principal phase.
Next, the respective alloy powders are put in a heat treatment furnace and the furnace is evacuated to 1.5xc3x9710xe2x88x925 Torr. Thereafter, while flowing H2 gas of 1 atmosphere into the furnace, the temperature is raised up to 730xc2x0 C. and maintained there for 30 min. Then, being evacuated again, and, after the degree of vacuum reaches 1.5xc3x9710xe2x88x925 Torr, the temperature is raised again to 800xc2x0 C. Thereafter, an Ar gas of 1 atmosphere is flowed into the furnace to cool rapidly the respective powders. By carrying out the X-ray diffraction of the respective obtained alloy powders, as a result of this, the respective powders are confirmed to have the Th2Ni17 type crystal phase as the principal phase.
Next, to make nitrogen included in the aforementioned respective alloy powders, the respective alloy powders are heat treated under a condition of 450xc2x0 C.xc3x9725 hours in the nitrogen gas atmosphere of 1 atmosphere. By this nitrogenization, the respective materials increased their weights by 3.0 to 3.9%. The composition, principal phase and average grain diameter of the obtained magnetic materials are shown in Table 1.
Thus obtained respective magnetic materials, after being mixed with an epoxy resin of 2.5% by weight, are molded under the compression condition of 1200 MPa, further cured at a temperature of 150xc2x0 C. for 2.5 hours to obtain the respective bonded magnets. The coercive force, residual magnetic flux density, and maximum magnetic energy product of the respective bonded magnets are shown in Table 1 as well.